It's possible that his return is being prepared without marking that someone else can claim him on his taxes. 

To make the adjustment and refile, follow these steps:

1. Open the tax return and select 'MY INFO' from your menu

2. Select the EDIT option (pencil) next to filers name

3. Scroll to question #3 and select 'YES' for the option someone else can claim me as a dependent on their tax return. 

4. Work through the rest of the section, review, and refile.